Can’t be bothered with keys but still need a way to prevent intruders from invading your fortress of solitude? Try a secret knock detector to guard your lair.
Don’t know how to build one? Stephen Hoefer over at Make demonstrates:
However, if you live in a shoebox New York City apartment like some of us, where everyone in the building can hear you knocking, this probably won’t be very helpful.
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Video: Stephen Hoefer / Made